content: /**
   * Copyright (c) 2016-present, RxJava Contributors.
   *
   * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
   * compliance with the License. You may obtain a copy of the License at
   *
   * http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software distributed under the License is
   * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
   * the License for the specific language governing permissions and limitations under the License.
   */
  
  package io.reactivex.observable.subjects;
  
  import java.util.concurrent.atomic.*;
  
  import io.reactivex.common.*;
  import io.reactivex.common.annotations.*;
  import io.reactivex.observable.*;
  
  /**
   * Represents a hot Single-like source and consumer of events similar to Subjects.
   * <p>
   * All methods are thread safe. Calling onSuccess multiple
   * times has no effect. Calling onError multiple times relays the Throwable to
   * the RxJavaPlugins' error handler.
   * <p>
   * The SingleSubject doesn't store the Disposables coming through onSubscribe but
   * disposes them once the other onXXX methods were called (terminal state reached).
   * <p>History: 2.0.5 - experimental
   * @param <T> the value type received and emitted
   * @since 2.1
   */
  public final class SingleSubject<T> extends Single<T> implements SingleObserver<T> {
  
      final AtomicReference<SingleDisposable<T>[]> observers;
  
      @SuppressWarnings("rawtypes")
      static final SingleDisposable[] EMPTY = new SingleDisposable[0];
  
      @SuppressWarnings("rawtypes")
      static final SingleDisposable[] TERMINATED = new SingleDisposable[0];
  
      final AtomicBoolean once;
      T value;
      Throwable error;
  
      /**
       * Creates a fresh SingleSubject.
       * @param <T> the value type received and emitted
       * @return the new SingleSubject instance
       */
      @CheckReturnValue
      @NonNull
      public static <T> SingleSubject<T> create() {
          return new SingleSubject<T>();
      }
  
      @SuppressWarnings("unchecked")
      SingleSubject() {
          once = new AtomicBoolean();
          observers = new AtomicReference<SingleDisposable<T>[]>(EMPTY);
      }
  
      @Override
      public void onSubscribe(@NonNull Disposable d) {
          if (observers.get() == TERMINATED) {
              d.dispose();
          }
      }
  
      @SuppressWarnings("unchecked")
      @Override
      public void onSuccess(@NonNull T value) {
          if (value == null) {
              onError(new NullPointerException("Null values are not allowed in 2.x"));
              return;
          }
          if (once.compareAndSet(false, true)) {
              this.value = value;
              for (SingleDisposable<T> md : observers.getAndSet(TERMINATED)) {
                  md.actual.onSuccess(value);
              }
          }
      }
  
      @SuppressWarnings("unchecked")
      @Override
      public void onError(@NonNull Throwable e) {
          if (e == null) {
              e = new NullPointerException("Null errors are not allowed in 2.x");
          }
          if (once.compareAndSet(false, true)) {
              this.error = e;
              for (SingleDisposable<T> md : observers.getAndSet(TERMINATED)) {
                  md.actual.onError(e);
              }
          } else {
              RxJavaCommonPlugins.onError(e);
          }
      }
  
      @Override
      protected void subscribeActual(@NonNull SingleObserver<? super T> observer) {
          SingleDisposable<T> md = new SingleDisposable<T>(observer, this);
          observer.onSubscribe(md);
          if (add(md)) {
              if (md.isDisposed()) {
                  remove(md);
              }
          } else {
              Throwable ex = error;
              if (ex != null) {
                  observer.onError(ex);
              } else {
                  observer.onSuccess(value);
              }
          }
      }
  
      boolean add(@NonNull SingleDisposable<T> inner) {
          for (;;) {
              SingleDisposable<T>[] a = observers.get();
              if (a == TERMINATED) {
                  return false;
              }
  
              int n = a.length;
              @SuppressWarnings("unchecked")
              SingleDisposable<T>[] b = new SingleDisposable[n + 1];
              System.arraycopy(a, 0, b, 0, n);
              b[n] = inner;
              if (observers.compareAndSet(a, b)) {
                  return true;
              }
          }
      }
  
      @SuppressWarnings("unchecked")
      void remove(@NonNull SingleDisposable<T> inner) {
          for (;;) {
              SingleDisposable<T>[] a = observers.get();
              int n = a.length;
              if (n == 0) {
                  return;
              }
  
              int j = -1;
  
              for (int i = 0; i < n; i++) {
                  if (a[i] == inner) {
                      j = i;
                      break;
                  }
              }
  
              if (j < 0) {
                  return;
              }
              SingleDisposable<T>[] b;
              if (n == 1) {
                  b = EMPTY;
              } else {
                  b = new SingleDisposable[n - 1];
                  System.arraycopy(a, 0, b, 0, j);
                  System.arraycopy(a, j + 1, b, j, n - j - 1);
              }
  
              if (observers.compareAndSet(a, b)) {
                  return;
              }
          }
      }
  
      /**
       * Returns the success value if this SingleSubject was terminated with a success value.
       * @return the success value or null
       */
      @Nullable
      public T getValue() {
          if (observers.get() == TERMINATED) {
              return value;
          }
          return null;
      }
  
      /**
       * Returns true if this SingleSubject was terminated with a success value.
       * @return true if this SingleSubject was terminated with a success value
       */
      public boolean hasValue() {
          return observers.get() == TERMINATED && value != null;
      }
  
      /**
       * Returns the terminal error if this SingleSubject has been terminated with an error, null otherwise.
       * @return the terminal error or null if not terminated or not with an error
       */
      @Nullable
      public Throwable getThrowable() {
          if (observers.get() == TERMINATED) {
              return error;
          }
          return null;
      }
  
      /**
       * Returns true if this SingleSubject has been terminated with an error.
       * @return true if this SingleSubject has been terminated with an error
       */
      public boolean hasThrowable() {
          return observers.get() == TERMINATED && error != null;
      }
  
      /**
       * Returns true if this SingleSubject has observers.
       * @return true if this SingleSubject has observers
       */
      public boolean hasObservers() {
          return observers.get().length != 0;
      }
  
      /**
       * Returns the number of current observers.
       * @return the number of current observers
       */
      /* test */ int observerCount() {
          return observers.get().length;
      }
  
      static final class SingleDisposable<T>
      extends AtomicReference<SingleSubject<T>> implements Disposable {
          private static final long serialVersionUID = -7650903191002190468L;
  
          final SingleObserver<? super T> actual;
  
          SingleDisposable(SingleObserver<? super T> actual, SingleSubject<T> parent) {
              this.actual = actual;
              lazySet(parent);
          }
  
          @Override
          public void dispose() {
              SingleSubject<T> parent = getAndSet(null);
              if (parent != null) {
                  parent.remove(this);
              }
          }
  
          @Override
          public boolean isDisposed() {
              return get() == null;
          }
      }
  }
  